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Fig. 4 Proposed biogenesis of zoanthamine shown in Fig. 4 [23]. A single carbon chain precursor (C1 to C24) could be cyclized to give a complex polycyclic structure, like 13. Meanwhile, feeding experiments with a labeled compound for zooxathellamine (21) have been examined, and a polyketide biosynthetic pathway has been supported [28].

Recently, a total synthesis of norzoanthamine (12) has been achieved using an intramolecular Diels-Alder reaction as a key step for constructing the requisite chiral triene [35]. This synthesis may be a powerful tool for advancing the study of norzoanthamine as a therapeutic drug.

Pinnaic Acids, Potent cPLA2 Inhibitors

Specific inhibitors of phospholipase A2 (PLA2) have been considered as potential drugs for the treatment of inflammation and other disease states, since PLA2 is linked to the initial step in the cascade of enzymatic reactions that lead to the generation of inflammatory mediators [36, 37]. Marine natural products such as manoalide [38] and luffariellolide [39] have been reported to be potent PLA2 inhibitors [40,41]. A cytosolic 85-kDa phospholipase (cPLA2) exhibits specificity for the release of arachidonic acid from membrane phospholipids [42-44]. Therefore, compounds that inhibit cPLA2 activity have been targeted as anti-inflammatory agents.

Pinnaic acid (24) and tauropinnaic acid (25) were isolated from the viscera of P. muricata [45]. Both 24 and 25 have a unique 6-azaspiro[4.5]decane moiety. The gross structure of 24 was also confirmed by a comparison of the EI-MS fragment peaks with the corresponding peaks of 25. The relative stereochemistry of 25 was deduced from phase-sensitive NOE correlations.